The present invention relates to the toner replenishment device of an electrophotographic image forming apparatus.
A high-speed image forming apparatus and color image forming apparatus involve a disadvantage that installation of a development device in the vicinity of a toner reservoir section to replenish a toner to the developing device is made difficult by the increased capacity of the toner reservoir section for reserving toner.
In a commonly known toner replenishment technique developed to solve this problem, the toner reservoir section and the developing device are arranged separately to each other, and a toner is conveyed from the toner reservoir section to the development device using the toner conveyance method known as an air conveyance method capable of conveying a toner over a great distance.
The toner replenishment device based on air conveyance is basically composed of a toner reservoir section including a toner mixing chamber, fluid conveyance means for conveying a fluid mixture of toner and air from the toner reservoir section, and a toner separation section for separating toner from the conveyed fluid mixture.
In many of the devices of this type, air separated from toner is led into the mixing chamber through the aforementioned fluid conveyance means, without allowing part of the air to be discharged to the outside.
A circulating type toner conveyance technique is also known, wherein a diaphragm pump is arranged on each of the forward and return conveyance paths so as to allow the aforementioned fluid mixture to be conveyed and returned (e.g. Patent Document 1 indicating Japanese Patent Tokkai 2000-137376).
A pressure fluctuation called pulsation occurs to the diaphragm pump by its very nature. When two diaphragm pumps are used, interference between the pressure fluctuations produced by each of the pump, with the result that pressure fluctuation are offset by each other, on the one hand. On the other hand, the pressure fluctuation is doubled when overlapped. Unless means are taken to place the pressure fluctuation under control, toner may be scattered out of the unit connections with the development device.
At the time of maintenance, the development device must be removed from the connection with the toner replenishment unit. To control the aforementioned scattering of toner, the connection of the unit can be sealed with rubber gasket, but this may cause poor workability at the time of maintenance. To avoid this problem, foamed urethane is used for sealing in many cases. According to this method, however, the strength of the sealing material will be overcome by pressure fluctuation so that toner will be scattered if there is a large pressure fluctuation.
Another method is to provide the aforementioned toner separation section with a filter so that part of air is released to the outside so as to adjust the air pressure. However, this method involves the need of filter replacement work, and causes earlier clogging of the filter. This may also cause toner to scatter. Further, a method of controlling the speed of each of the motors for driving two pumps or a method of controlling the conveyance flow rate of the fluid mixture sent from two pumps is also proposed (e.g. Patent Document 1 mentioned above).
The pump motor speed, however, is about 2,000 through 5,000 rpm. It is extremely difficult to control the speed in such a way that the two motor speeds will be equal to each other. Such a method is insufficient to provide a reliable solution to the problem. Accordingly, it is not easy to reduce this pressure fluctuation.